1. Field of the Invention
The present invention relates to a suede artificial leather having excellent color fastness to light and color development in a wide variety of colors and having a high quality with a good suede feeling, surface touch and hand, and further relates to a semi-grained or grained artificial leather made of the suede artificial leather.
2. Description of the Prior Art
Suede artificial leathers comprising superfine fibers and an elastomeric polymer have been conventionally known. These suede artificial leathers made of superfine fibers are highly appreciated as materials analogous to natural leathers because of their excellent suede feeling and surface touch. To color the suede artificial leathers, dyes have been conventionally used.
However, the superfine fiber is much poor in the color development as compared with fibers of ordinary fineness because of its small fineness. Therefore, several to about 20 times amount of dye as compared with the fibers of ordinary fineness is required for the color development of the superfine fiber, this making the color fastness to rubbing and the color fastness to light of the superfine fibers poor. The elastomeric polymer contained in the suede artificial leathers is much poor in the color fastness to light as compare with the fiber, this being a major cause to deteriorate the color fastness to light of the suede artificial leather itself It has been conventionally considered to improve the color fastness to light of the dye itself, but there is a limit to the improvement. At present, a little is provided as suede materials which meet severe requirements of users in the applications requiring a long-term stability under severe conditions as in the case of car seats, etc. If any, the obtainable colors thereof are largely limited.
Although the strong demand continues for the artificial leathers excellent in the color development, the color fastness to light and the color fastness to rubbing in a wide variety of colors, the attempts to solve the problems by conventional approaches utilizing the color development of dyes has reached the limit.
To solve the problems, several coloring methods using pigments which are superior to dyes in the color fastness to light have been proposed. For example, Japanese Patent Publication No. 62-37252 discloses on pages 1-4 a method using superfine fibers colored by incorporating a pigment into a fiber-constituting polymer. Japanese Patent Application Laid-Open Nos. 5-331782 (pages 2-4) and 2000-45186 (pages 1-7) disclose methods for dying superfine fibers colored by incorporating a pigment into a polymer. Although the light resistance of fibers is improved by these methods, the improvement of the light resistance is limited because nothing is considered on preventing the deterioration in the light resistance of the elastomeric polymer. In addition, since no pigment is added to the elastomeric polymer, the elastomeric polymer is whitened to make the color difference between the fiber and the elastomeric polymer remarkable, thereby making it difficult to obtain suede artificial leathers with high quality. Pigments include organic pigments, carbon black and inorganic pigments. The proposed methods include a process where one of the components of superfine fiber-forming fibers is removed by an organic solvent or a process where the elastomeric polymer dissolved in a solvent is wet-coagulated in a liquid containing an organic solvent, each being employed in the conventional method for producing artificial leathers. As a result of the experiments made by the inventors, it was found that an organic pigment in superfine fiber-forming fibers was partly eluted into the organic solvent in the superfine fiber-forming process or the wet coagulation process. Therefore, carbon black and the inorganic pigments must be mainly used as the pigment in the industrial productions, this narrowing the range of obtainable colors and resulting in a poor color development and brilliantness.
In the method of Japanese Patent Publication No. 62-37252, it is attempted to attain a variety of colors by incorporating pigments only into the fiber. However, this method requires to switch the spinning apparatuses to increase the production loss, this making the method difficult to be industrially practiced. In addition, this method cannot attain a sufficient color development because of a poor color development of the superfine fibers. If a large amount of pigment is incorporated to enhance the color development, the spinning becomes difficult because of the clogging of filter and the increase in spinning pressure and the properties of the resultant fibers are largely deteriorated.
Other known color developing methods include a method where superfine fibers colored by incorporating a pigment such as carbon black into a fiber-constituting polymer are dyed, and a method where an elastomeric polymer colored by incorporating a pigment such as carbon black thereinto is dyed (for example, Japanese Patent Application Laid-Open Nos. 2002-146624 (pages 2-7) and 2001-279532 (pages 2-7)). The proposed methods intend to darken the color of substrate by making the developed color of dye blackish with carbon black, and the improvement of the color fastness to light by these methods is limited.
In another proposed method, a nonwoven fabric for forming superfine fibers is provided with an elastomeric polymer containing a pigment and then dyed (for example, Japanese Patent Application Laid-Open Nos. 63-315683 (pages 1-6) and 58-197389 (pages 1-4)). In these methods, the fastness to light is improved for the elastomeric polymer, but limited for the superfine fibers because they are colored only with dyes. In addition, the proposed methods include a process where one of the components of superfine fiber-forming fibers is removed by an organic solvent and a process where the elastomeric polymer dissolved in a solvent is wet-coagulated in a liquid containing an organic solvent, each being employed in the conventional method for producing artificial leathers. As a result of the experiments made by the inventors, it was found that an organic pigment in superfine fiber-forming fibers was partly eluted into the organic solvent in the superfine fiber-forming process or the wet coagulation process. Therefore, carbon black and the inorganic pigments must be mainly used as the pigment in the industrial productions, this narrowing the range of obtainable colors and resulting in a poor color development and brilliantness. Further, these methods are mainly intended to provide a nap-raised sheet with iridescent color tone or uneven pattern by utilizing the color difference between the fiber and the elastomeric polymer, which is different from the suede artificial leather intended by the present invention.
Further proposed are several methods where a fiber sheet is impregnated with an elastomeric polymer blended with a pigment having a low infrared absorbancy, and then dyed (for example, Japanese Patent Application Laid-Open Nos. 5-321159 (page 2), 7-42084 (page 2), 2002-242079 (page 2) and 2002-327377 (page 2)). In these methods, the elastomeric polymer is colored black by a low infrared-absorbing organic black pigment such as azomethineazo compounds and perylene compounds or the elastomeric polymer is colored to blackish color with a low chroma by a mixture of three organic pigments, in place of using carbon black which is easy to build up heat by the absorption of infrared ray. Thus, these methods are intended to make the elastomeric polymer into blackish color thereby to darken the color developed by dye. However, since the superfine fibers are colored only with dye, the improvement of the color fastness to light is limited. In any of the proposed methods, the solvent-type polyurethane blended with a pigment is wet-coagulated. As mentioned above, since the organic pigment in the elastomeric polymer is partly dissolved into the organic solvent in this process, the organic pigment is partly released to cause color variation and the switching loss is increased, thereby failing to attain industrially stable productivity. Further, the low infrared-absorbing organic pigment is quite expensive, this being unfavorable in view of production costs and limiting the usable pigments to make it difficult to obtain a wide variety of colors.
A coloring method by adsorption of pigment in a water bath, i.e., a pigment exhaustion coloring method is also proposed (for example, Japanese Patent Application Laid-Open Nos. 2001-248080 (pages 2-6) and 10-259579 (pages 2-5)). These methods provide a relatively good color fastness to light. However, since the pigment is fixed to the surface of fibers and elastomeric polymer and not embedded in fibers and elastomeric polymer, the pigment is easily released to likely deteriorate the fastness such as the color fastness to rubbing. Particularly in superfine fibers of 0.2 dtex or thinner, a large amount of pigment is required as in the case of dyeing to result in a deterioration of the fastness such as the color fastness to rubbing.
In summary, the proposed methods for coloring by pigments involves the following drawbacks.    (1) The methods employ a process where one of the components of superfine fiber-forming fibers is removed by an organic solvent and/or a process where the elastomeric polymer dissolved in a solvent is wet-coagulated in a liquid containing an organic solvent, each employed in the conventional method for producing artificial leather. Therefore, carbon black and the inorganic pigments must be mainly used as the pigment in industrial production, this limiting the range of obtanable colors and resulting in a poor color development and brilliantness. If organic pigments are used, the organic pigments are released in the processes using an organic solvent, failing to achieve an industrially stable productivity.    (2) Since pigments are incorporated into only one of fiber and elastomeric polymer, the methods bring about only a limited improvement to the color fastness to light, and also, bear problems in the color fastness to rubbing and the range of obtainable colors.    (3) The methods give substantially no consideration for the problems associated with the coloring by pigments, i.e., the deterioration in mechanical properties and various fastness such as the color fastness to rubbing. Therefore, it is hard to consider that the proposed methods are satisfactory in mechanical properties and fastness.
Thus, no suede artificial leather having excellent color fastness to light and color development in a wide variety of colors and also excellent in suede feeling, surface touch, hand, mechanical properties and various fastness has been industrially provided.